Rheostatic switch



May 13, 1952 R w, McGARVEY 2,596,420

RHEOSTATIC SWITCH Filed Aug. 10, 1950 INVENTOR.

ATTORNEY Patented May 13, 1952 RHEOSTATIC SWITCH Robert W. McGarvey, Detroit,'Mich assignor to Victor A. Wicks and Ford J. Dupure, both of Dearborn, Mich.

Application August 10, 1950, Serial No. 178,674

2 Claims.

This invention relates to rheostatic switches and in particular to improvements in powdered carbon type rheostatic switches.

The primary object of the invention is to provide an improved powdered carbon type variable rheostatic switch which is accurate and sensitive, which will not become ineffective through repeated use, which maintains constant resistance at any given point of travel of the movable element, and which maintains uniformity of its variable resistance at all points during both its make and break operation.

Another object of the invention is to provide a rheostatic switch of the class described which has an extremely long life, requires no servicing, which can be operated manually, mechanically or thermostatically, which is inexpensive to manufacture, and which is adaptable to many uses wherein rheostatic control or combined rheostatic and off and on control of circuits is desirable or required.

Other objects of the invention will become apparent by reference to the following detailed description taken in connection with the accompanying drawing, in which:

Fig. l is a vertical sectional view through a rheostatic switch embodying the invention.

Fig. 2 is a horizontal sectional view taken on the line 2-2 of Fig. 1.

Fig. 3 is a vertical sectional view similar to Fig. 1 showing an alternate embodiment of the invention.

Fig. 4 is a horizontal sectional View taken on the line 44 of Fig. 3.

Fig. 5 is a view part in section and part in elevation showing the resilient compressible cylinder employed in the embodiment of the invention disclosed in Figs. 1 and 2.

Fig. 6 is a view part in section and part in elevation showing the resilient compressible cylinder employed in the embodiment of the invention described in Figs. 3 and 4.

Referring now to the drawings wherein like numerals refer to like and corresponding parts throughout the several views, the particular embodiment of the invention disclosed in Figs. 1, 2 and 5 comprises, in general, a cylindrical capsule I0 closed at its bottom end I00 and open at its top end, a resilient compressible cylinder I I preferably formed of rubber, silicon rubber or other material or combination of materials which is heat resistant, nonconductive and yet will spring back to its normal size and shape after axial compression, the said cylinder I I having a central axial aperture I2 therethrough preferably smaller at the lower end I20 thereof and is provided with inner circumferential grooves I3 and IA near the top and bottom thereof extending radially outward from the said central axial aperture I2, a movable contact I5 and fixed contact I6 positioned in the said inner circumferential grooves I3 and I4, the said movable contact I5 comprising a disc I50 positioned in the upper inner circumferential groove I3, a central elongated tapered contact point I5I and a contact head I52, the said fixed contact I6 comprising a disc I positioned in the lower inner circumferential groove I4 and a contact head IIiI extending through the lower end I20 of theaxial aperture I2 of the cylinder II into contact with the bottom end I00 of the capsule I0, and powdered or finely ground carbon I1 disposed in the, axial aperture I2 of the cylinder II between the discs I50 and I60 of the movable and fixed contacts I5 and I6 respectively.

A piston I8 or some other suitable means is employed for manually, mechanically or thermostatically compressing the resilient cylinder I I in thedirection indicated by the arrow 20 and moving themovable contact I5 toward and into contact with the fixed contact IS with the contact point I5I of the movable contact I5 in engagement with the fixed contact I5.

In the illustrative embodiment shown in Figs. 1, 2 and 5, the piston I8 contacts the contact head [52 of the movable contact I5 as well as a fiber or other washer I9 disposed around the said contacthead I52 of the movable contact I5. This construction assures uniform compression and movement of the resilient cylinder II and the movable contact I5 within the capsule I0 responsive to movement of the piston I8 in the direction illustrated by the arrow 20. When pressure on the piston I8 moving it in the direction indicated by the arrow 20 is released, the resilient compressiblecylinder II returns itself and the piston I8 to their normal position assumed prior to the application of pressure on the piston I 8. A lead 2I connected to the piston I8 provides an electrical connection to the movable contact I5 through the said piston IS. A lead 22 connected to the capsule I0 provides an electrical connection to the fixed contact I 6 through the said capsule I0.

When a rheostatic switch embodying the invention is connected in an electric circuit, and the movable contact I5 is in its normal position as shown in Fig. 1, the. resistance between the movable and fixed contacts I5 and I6 is so great that practically no current passes through the 3 powdered or finely ground carbon II. As the piston I8 compresses the resilient compressible cylinder I I, the movable contact I moves toward the fixed contact I6 compacting the powdered or finely ground carbon I! while the elongated tapered contact point I5I of the movable contact I5 approaches the fixed contact I6, and the resistance between the movable and fixed contacts I is progressively lessened whereby the current passing through the powdered or finely ground carbon II progressively increases until, when the pointed end of the tapered contact point I5I of the movable contact I5 contacts the fixed contact I6, substantially full current is passing through the powdered or finely ground carbon I1 thereby eliminating any arcing of the contacts I5 and I6 during the make and break thereof.

Upon release of the piston I8, the resilient compressible cylinder II progressively returns from its compressed position to its normal position shown in Fig. 1 with a corresponding progressive decrease in current passing between the contacts I5 and IS. The slight roughness of the inside surface 23 in the resilient compressible cylinder II as indicated in Fig. 5 causes a movement of the granules of the carbon II during axial movement of the resilient cylinder II whereby to prevent fixation of permanent caking of the carbon granules. This assures the granules of the carbon II following the tapered point I50 of the movable contact I5 and a constant resistance at any given point in the movement of the movable contact I5.

The embodiment of the invention disclosed in Figs. 3, 4 and 6 is like and similar to the embodiment of the invention disclosed in Figs. 1, 2 and 5 except that the inside surface of the resilient compressible cylinder II is provided with a plurality of radially disposed circumferential grooves 230 creating a very rough or ribbed inside surface in the resilient compressible cylinder I I which causes a greater and more positive movement of the granules of the carbon IT by mechanically activating the same whereby to prevent fixation or permanent caking thereof by causing the carbon granules to work during the movement of the tapered point I50 of the contact I5 thereinto and therefrom.

The proportioning of the tapered point I50 of the contact I5 with respect to the volume and fineness of the granules of the carbon IT, and the distance between the movable contact I5 and the fixed contact I6 determines the characteristics of rheostatic switches embodying the invention. The size of the rheostat and volume and fineness of carbon granules employed dictates the extent to which the inner surface of the compressible cylinder II is roughened or otherwise deformed.

Although but a single embodiment of the invention and one modification thereof have been disclosed and described in detail, it is obvious that many changes may be made in the size,

shape, arrangement and detail of the elements of the invention and the proportioning thereof without departing from the spirit and scope thereof as defined by the appended claims.

I claim:

1. A rheostatic switch comprising a capsule, a resilient compressible element having an aperture axially therethrough disposed in the said capsule, a pair of contacts disposed in axial spaced relationship in said resilient compressible element, one of said contacts including an axially tapered contact point disposed toward the other contact whereby to contact the same when the said resilient compressible element is axially compressed, and finely ground carbon disposed in the said axially disposed aperture in the resilient compressible element between the said contacts, the inner surface of the said resilient compressible element at the axial bore therethrough between the said contacts being provided with a plurality of deformations between the said contacts whereby to mechanically engage and activate and cause turbulence in the said carbon granules and prevent caking thereof during axial compression and expansion of the said resilient compressible element.

2. In a rheostatic switch, a resilient compressible element having an aperture axially therethrough, the said compressible element having a pair of axially spaced circumferentially disposed grooves therein communicating with the said axial aperture therethrough, a pair of contacts disposed in said axial spaced grooves in said resilient compressible element, one of said contacts including an axially tapered contact point disposed toward the other contact whereby to contact the same when the said resilient compressible element is axially compressed, and finely ground carbon disposed in the said axially disposed aperture in the resilient compressible element between the said contacts, the inner surface of the said resilient compressible element at the axial bore therethrough between the said contacts being circumferentially ribbed whereby to mechanically engage and activate and cause turbulence in the said carbon granules and prevent caking thereof during axial compression and expansion of the said resilient compressible element.

ROBERT W. MCGARVEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 787,089 Fahrney Apr. 11, 1905 1,741,802 Zimmerman Dec. 31, 1929 FOREIGN PATENTS Number Country Date 243,143 Great Britain Nov. 26, 1925 

